Page:The Zoologist, 4th series, vol 4 (1900).djvu/359

Rh ores of the country being green. We must, therefore, assume that assimilative colouration, as here understood, signifies a close similarity of colouring between an organism and its environment, due to the direct action of the latter upon the organism, either through nerve stimuli or through the direct absorption of the environment into its system, such colouring being essentially non-significant, any utility it may possess being entirely fortuitous.

The general proposition that in the earliest ages of the earth's history such assimilative colouration everywhere prevailed is a perfectly legitimate surmise, though a mere surmise it must ever remain. But, on the other hand, while even the most advanced selectionists will doubtless allow that the earliest organic colour, or colours, were probably non-significant, they would be quite justified in opposing the hypothesis of assimilation, as above defined, on the ground that there is no reason whatever to suppose that the direct action of any environment upon an organism must necessarily produce in it a colouration identical with that of its environment; and Mr. Distant's own examples might be cited in support of this contention, e.g., that a diet of hemp-seed turns Bullfinches black; that red and yellow feathers are produced in certain Green Parrots by feeding them on fish; that the feathers of Cotinga can be transformed from purple to brilliant red by the application of heat, and so forth—in all of which instances there is no colour similarity between the various causes and their effects; and still further experimental evidence might be adduced. Indeed, when we consider the numerous instances of non-significant colours known to us both in the organic and inorganic worlds, there can be no reasonable objection to the hypothesis that the earliest organisms might have developed, through purely physico-chemical causes, non-significant colours, both brilliant and otherwise, which might, or might not, have corresponded with those of their respective environments; and thus, when natural selection did become a vera causa, there would already have been a considerable range of colour upon which it might operate. However, with regard to the first appearance of this factor, it seems more reasonable to suppose that this was practically synchronous with the first appearance of organic life, though the struggle for existence at that period would be solely against the physical forces of nature, and thus natural selection would then have little or no effect upon colouration, except perhaps indirectly.

Supposing, however, that, for the sake of argument, we agree to accept Mr. Distant's general suggestion, we have yet to consider the correctness of his corollary thereto, which is really the essential portion of his paper. According to this view: "If the earliest forms of life are to be sought only in